Using LaTeX

There is a help page here

However you use double square brackets and the formulas are set up like this

[math] (remember the double square brackets though)
\dfrac {3x^3-4x^2+3x-4} {x^4-2x^2+5}
[math]

gives
$\dfrac {3x^3-4x^2+3x-4} {x^4-2x^2+5}$

[math]
area=\pi r^2
[math]

gives
$area=\pi r^2$

[math]
\sqrt {\frac {1}{3x} y^5-3}
[math]

gives
$\sqrt{ \frac {1}{3x} y^5-3}$

[math]
\left[ \dfrac {1}{3x} y^5-3 \right]
[math]

gives
$\left[ \dfrac {1}{3x} y^5-3 \right]$